This study is of the early interactions and fate of an arbovirus in susceptible and refractory mosquitoes in order to characterize those factors which control or influence the efficiency and/or specificity of virus invasion to, and through, cells of the gut to sites where biological transmission can later occur. More specifically, the proposed studies are directed to following the early fate of the arbovirus in the juices of the gut lumen, efficiency of survival, penetration and entry to the gut cells, subsequent replication, and the mechanism of transfer to other susceptible cells of the vector mosquito. We propose to use techniques established in our laboratory which will quantitatively evaluate these events at the cellular and molecular level in vivo, with similar biological activities monitored and compared in in vitro tissue culture systems. These studies will be followed by correlating electron microscopy and various techniques of molecular biology designed to follow the fate of macromolecules in biological systems. An investigation of these complex interactions in vivo as compared with known in vitro interactions may allow a more thorough understanding of the factors controlling and specifying arbovirus transmission by vector mosquitoes so that new and potentially more effective systems of biological control, or other may be effected and/or evaluated.